This invention relates to a float-type flowmeter for measuring the flow of fluids, incorporating a measuring tube through which measuring tube the fluid can flow against the force of gravity and which encompasses a float that is movable at least in the flow direction.
This invention further relates to a method for the predictive status indication of a float-type flowmeter for moving fluids which float-type flowmeter incorporates a measuring tube through which the fluid can flow against the force of gravity and which encompasses a float that is movable at least in the flow direction.
Float-type flowmeters have been used since the middle of the last century for measuring the flow volume in enclosed pipelines. To this day, they are still employed in many flow-measuring systems in the chemical and process industries.
In its simplest form, a float-type flowmeter consists of a conical measuring tube and a floating element. The fluid whose flow rate is to be determined flows through the measuring tube against the force of gravity, i.e. in an upward direction. The measuring tube is a conical tube whose flared upper end accommodates a suitably configured float which is freely movable at least in the direction of the flow and which in conjunction with the measuring tube constitutes a metering valve. The density of the float is greater than that of the fluid traveling through the measuring tube. As a function of the flow rate, the float will be suspended in the measuring tube at a particular height level which is determined by the equilibrium between the hydrodynamic force of the moving fluid impinging on the float and the difference in the weight or buoyancy parameters of the float. That height level of the float, also referred to as the float lift, can be either viewed and read directly off a graduated scale on a transparent measuring tube or transmitted for instance via a magnetic coupling for display on an external gauge and/or an electrical meter.
Even in its suspended state in which a constant flow rate keeps the float balanced at a certain lift level, the float does not stand perfectly still but oscillates at least one cycle in the direction of the flow and in the opposite direction. In addition, it is also typical for the float to oscillate in a direction perpendicular to that of the flow as well as along a rotational pattern. This phenomenon is utilized in a float-type flowmeter described in the German patent DE 196 24 974 C1 in that the amplitude, i.e. the maximum deflection of the float, is measured and analyzed and an error or alarm signal is generated when the amplitude of the float falls below a minimum setpoint value. The error or alarm signal indicates a malfunction of the float-type flowmeter, i.e. a jamming of the float in the measuring tube. This earlier design of a float-type flowmeter thus permits the instantaneous detection of a mechanical blockage of the float, avoiding a situation where the lift of a jammed float is erroneously interpreted as representing the actual flow rate.
The prior-art float-type flowmeter described above thus utilizes the oscillatory motion of the float for the detection of a blocked float in a non-transparent measuring tube where visual observation of the float in the measuring tube is not possible. One drawback of this prior-art design of a float-type flowmeter lies in the fact that an error or alarm signal is not triggered until the malfunction of the float-type flowmeter actually occurs. By then, quite possibly, too low or too high a flow rate of the fluid may already have led to damage in the pipeline or in the system connected to it.
In view of the above, it is the objective of this invention to introduce a float-type flowmeter, as well as a method for predictive status indication for a float-type flowmeter, permitting the indication of progressive deterioration and possibly impending malfunction of the float-type flowmeter.
According to the invention, the float-type flowmeter solving the problem referred to above is characterized in that it is provided with a detection system which permits the tracking of the float movement, the generation of a motion signal corresponding to the movement of the float, the transmission of this float-movement motion signal to a predictive state-evaluation unit, the comparison in the predictive state-evaluation unit of the motion signal with anticipated values for the float movement, and, based on any deviation of the motion signal from the said anticipated values, the generation and output by the predictive state evaluation unit of information relative to the probable condition of the float-type flowmeter that is to be expected as time progresses.
The predictive method according to this invention for determining the condition of a float-type flowmeter, solving the problem referred to above, is characterized in that the movement of the float is captured in the form of a motion signal which corresponds to the movement of the float and which is compared to anticipated float-movement values, and that, on the basis of any deviations of the motion signal from the anticipated values, information is generated and output relative to the probable condition of the float-type flowmeter that is to be expected as time progresses.
For the purpose of both the float-type flowmeter according to this invention and the predictive status indication method for a float-type flowmeter, the motion signal reflecting the movement of the float is utilized in its entirety. This motion signal is a time-related signal which indicates both the deflection of the float from its home position as a function of time and any possible rotational movement of the float. Thus, according to this invention and in contrast to prior art, not only the amplitude i.e. the maximum deflection of the float but the time signal describing the entire movement of the float is continually acquired and processed. It follows that, as provided for by the invention, the motion signal representing the movement of the float can be compared in continuous and multifaceted fashion with the the values anticipated for this signal, as explained in the following example.
But first it should be emphasized once again that the capabilities of the float-type flowmeter according to this invention and the predictive status indication method of this invention for a float-type flowmeter are not limited to the detection and indication of an already occurring malfunction such as a blockage of the float. Rather, the invention makes it possible to predict a condition of the float-type flowmeter that is to be expected at a future point in time. Accordingly, the user of a float-type flowmeter according to this invention is alerted relative to a malfunction to be expected when there is still time to avert such malfunction altogether by taking appropriate measures. The invention thus helps not only to detect a system failure but to prevent it in the first place.